Issue #3495678: Add a fallback for the config option

src/Oauth2ScopeProviderFactory.php

@@ -53,7 +53,7 @@ class Oauth2ScopeProviderFactory implements Oauth2ScopeProviderFactoryInterface
    * {@inheritdoc}
    */
   public function get(): Oauth2ScopeAdapterInterface {
-    $plugin_id = $this->config->get('scope_provider');
+    $plugin_id = $this->config->get('scope_provider') ?? 'dynamic';
     /** @var \Drupal\simple_oauth\Plugin\ScopeProviderInterface $plugin */
     $plugin = $this->scopeProviderManager->getInstance(['id' => $plugin_id]);
     $adapter = $plugin->getScopeProviderAdapter();